More than half of calls to U.S. poison control centers about energy drinks like Red Bull and Monster are for children younger than 6, some suffering seizures and heart problems, according to a new study.

The study supports the contention that energy drinks aren’t safe for children and should carry explicit risk warnings, said Steven Lipshultz, chairman of pediatrics at Wayne State University in Detroit. People of all ages with underlying health conditions should be vigilant about the heavily caffeinated beverages, he said. The data was presented Sunday at the American Heart Association’s annual meeting in Chicago.

“Exposure to energy drinks is a continuing health problem,” said Lipshultz, who is also pediatrician-in-chief at Children’s Hospital of Michigan. “You normally think of teens and young adults as most likely to drink them, but we found that half of calls to U.S. poison control centers involved unintentional exposures by children less than 6 years old.”

The researchers analyzed all 5,156 calls to poison control centers from October 2010 to September 2013 involving energy drinks. Most of the calls for children younger than 6 were because they got the ­beverages accidentally. Nearly a third had serious symptoms requiring treatment, including tremors or seizures, nausea and vomiting or chest pain and erratic heart rhythms.

The Food and Drug Administration began an investigation into caffeinated energy drinks in 2012 after reports of increasing emergency room visits tied to the drinks. The American Medical Association has called for limiting sales for people under age 18. .

Kids who are vulnerable

Young children, especially those with other health problems like heart disease or seizure disorders, may be particularly vulnerable. More common and less obvious conditions, like a predisposition to diabetes or attention deficit hyperactivity disorder, may make children more ­sensitive to the drinks, particularly if they are taking medicine, Lipshultz said.

Adults can face risks, as well. Drinkers ages 20 and older were the most likely to report serious side effects, particularly when they combine the drinks with alcohol, the study found.

Monster Beverage Corp. and closely held Red Bull GmbH didn’t return phone calls or e-mails seeking comment. Monster has previously said it doesn’t market its products to children and that its energy drinks aren’t highly caffeinated.

The drinks are sold as dietary supplements and aren’t tightly regulated. Because of that, it can be difficult to know how much caffeine they contain. Some include pharmaceutical-grade caffeine powder plus more from plant leaves and other sources, Lipshultz said.

“This has no place in the diet of children and teenagers, and it shouldn’t be marketed at all to those under 18,” he said.